With the development of communications technologies, in order to meet a requirement for a high-rate data service and an ultra-large capacity, a signal bandwidth of wireless communications will continually increase fast in the future. A fast increasing requirement for bandwidth brings a severe challenge to design of a radio transmitter, and in particular, to design of a power amplifier (PA) of a radio frequency front end, because the power amplifier needs to run with high efficiency while maintaining high linearity, and efficiency and linearity usually conflict with each other in design of a common power amplifier. Based on what is described above, digital predistortion (DPD) is a key technology for compensating non-linearity of a power amplifier in a digital domain, and can avoid losing linearity when the power amplifier works in a saturation state with high efficiency.
Currently, common used DPD models are models such as a series of simplified Volterra series-based (Volterra series) models, for example, a memory polynomial (MP), a generalized memory polynomial (GMP), and a dynamic deviation reduction-based Volterra series (DDR). Although these DPD models have simple structures, high accuracy and relatively easy parameter extraction, these DPD models are all polynomial-based time-domain models, which can be implemented in a narrowband system, for example, a fifth-order MP model requires that an output sampling signal bandwidth is five times of an input signal bandwidth; however, it is difficult to implement in a future ultra-wideband system. For example, in the LTE-Advanced, an input signal bandwidth is 100 MHz, and according to a requirement of a common used DPD model, the DPD model needs to output a sampling bandwidth of at least 500 MHz, which cannot be implemented. The signal bandwidth described by the DPD model increases when an order of a non-linear function in the DPD model increases because an existing DPD model uses Volterra series operators to construct the non-linear function. For this type of DPD model, only when an actual input bandwidth and output bandwidth match a signal bandwidth described by the model, the DPD model is accurate. For example, if a power amplifier generates fifth-order intermodulation distortion, a bandwidth of a collected output signal at an output end of the power amplifier is not less than five times of an input bandwidth, that is, if a signal output by the power amplifier can be collected completely, effective compensation may be performed on a characteristic of the power amplifier by using a model with fifth-order polynomial operators.
However, in the future ultra-wideband system, a signal output by the power amplifier usually cannot be collected completely because of a limitation on a bandwidth of a feedback channel and a sampling rate of an analog to digital converter (ADC). Usually, only a part of out-of-band signals can be collected. In this case, an existing DPD model has a great limitation, because the signal bandwidth described by the DPD model cannot match the bandwidth of the collected output signal, thereby causing inaccuracy of predistortion parameters calculated by using the DPD model and the collected signal, that is, appropriate predistortion cannot be performed on a signal, which also cannot enable an output signal to be a non-distortion signal.
Therefore, in an existing implementation manner, for predistortion processing, if predistortion accuracy needs to be ensured, a bandwidth of a collected feedback signal needs to be consistent with a bandwidth of intermodulation distortion generated by the adopted DPD model as much as possible. In this case, a requirement for a bandwidth and a sampling rate of a predistortion feedback channel is relatively high, thereby increasing a predistortion cost; and if the requirement for a bandwidth and a sampling rate of a predistortion feedback channel is lowered, although the predistortion cost is lowered, predistortion accuracy cannot be ensured.